Tracheal tube assemblies

ABSTRACT

A tracheal tube assembly comprises an outer tube and an inner cannula that is insertable within and removable from the outer tube. The inner cannula has an inner surface of a flexible plastic material such as PVC to which respiratory secretions cling. The outer surface of the cannula is of a material having a lower friction than the inner surface and may be a helical filament or a continuous layer. The machine end of the inner cannula projects beyond the outer tube to form a flexible portion which is terminated with a coupling.

BACKGROUND OF THE INVENTION

This invention relates to tracheal tube assemblies of the kind having anouter tube and an inner cannula that is insertable within and removablefrom the outer tube.

With such assemblies, the inner cannula is removed and replacedperiodically when secretions have built up on the cannula to an extentthat there is a risk of blockage. Tracheal tube assemblies aredescribed, for example, in U.S. Pat. No. 3,948,274, GB 2056285B, GB1099277, GB 125754, WO 90/04992, FR 2539998A, DE 72467, DE 1268313, EP0107779A, U.S. Pat. Nos. 4,817,598, 3,659,612, 4,009,720, 3,088,466,4,315,545, 2,765,792, 3,169,529, 3,263,684, 3,334,631, 3,587,589,3,688,774, 3,731,692, 3,889,688, 3,948,273, 3,973,569, 3,987,798,4,033,353, 4,045,058, 4,235,229, 4,471,776, 4,593,690.

In order to ensure as large as possible bore through the assembly, thewall of the inner cannula must be as thin as possible and the externaldiameter of the inner cannula must be as close as possible to theinternal diameter of the outer tube. This, however, increases the riskof kinking of the cannula on insertion, especially where friction withthe outer tube causes a greater axial force to be exerted on thecannula. A further problem arises because, if the cannula is made of alow-friction material, these tend not to enable respiratory secretionsto cling to them readily, thereby increasing the risk that secretionswill become dislodged and fall into the bronchi and lead to infection.

It is an object of the present invention to provide an improved innercannula for a tracheal tube assembly.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided atracheal tube assembly of the above-specified kind, characterized inthat the inner cannula has an inner surface to which respiratorysecretions will cling, and an outer surface of a different material witha lower coefficient of friction than the inner surface.

The outer surface may be a continuous layer of a filament extendingaround the outside of the cannula. The filament may extend helicallyaround the tube and may be of a metal. Alternatively, the outer surfacemay be provided by a low friction plastics material. The inner surfaceis preferably smooth and may be of a flexible plastics material such asPVC. The machine end of the inner cannula may project beyond the machineend of the outer tube and provide a flexible portion, the inner cannulahaving a coupling on its machine end.

BRIEF DESCRIPTION OF THE DRAWINGS

A tracheal tube assembly including an inner cannula, in accordance withthe present invention, will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a partly sectional side elevation view of the assembly;

FIG. 2 is a cross-section to a larger scale of a part of the innercannula; and

FIG. 3 is a cross-section of an alternative inner cannula.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first to FIG. 1, the assembly comprises an outertracheostomy tube 1 and an inner cannula 2.

The tracheostomy tube 1 is of conventional construction having a patientend 10 which, in use, is located in the patient's trachea and has aninflatable cuff 11 that seals the tube with the trachea. The machine end12 of the tube 1 extends at approximately right angles to the patientend, there being an abrupt bend portion 13 between them. A flange 14 islocated at the machine end 12 where it emerges from the tracheostomy atthe surface of the patient's neck and to which it is secured by a tape(not shown).

With reference now also to FIG. 2, the inner cannula 2 comprises aninner flexible tube 20 of PVC which has a circular section and a smoothinternal bore 15. Around the external surface of the tube 20 extends afilament in the form of a helical coil 21 of stainless steel wire. Thecoil 21 is secured to the external surface of the tube 20 and may bepartly embedded in it, providing that the outer surface of the coil isexposed.

A filament of other low friction materials, such as a low-frictionplastics could be used. The filament need not be wound in a helical coilbut could extend around the inner tube by being a part of a braidedsleeve.

The thickness and nature of the inner tube 20 is such that, by itself,it would be very prone to radial deformation and kinking. It also has arelatively high coefficient of friction which would make insertion inthe outer tube 20 difficult, especially in view of the fact that theexternal diameter of the inner cannula should be as close as possible tothe internal diameter of the tube 1. The coil 21, however, serves twopurposes. Firstly, it gives the cannula 2 radial rigidity so that it isimmune from kinking in normal use. Secondly, the wire coil 21 has arelatively low coefficient of friction so that it provides the exteriorof the cannula with a surface that can slide readily along the inside ofthe outer tube 1. This enables the inner tube 20 to be made of amaterial such as PVC to which respiratory secretions will cling butwhich has a relatively high coefficient of friction. Various differentfactors determine the degree to which secretions will cling to the innertube 20. For example, a highly polar material will improve adhesion aswill the presence of microscopic surface formations. A hydrophilicmaterial may also provide a better site for adhesion of the secretion.The flexible nature of the inner tube 20 and the coil 21 means that theinner cannula can have a high radial rigidity but be highly flexible,enabling it easily to be pushed through the outer tube 1 around theabrupt bend portion 13. It is also advantageous that the bore 15 of theinner cannula 2 be as smooth as possible so as to reduce turbulence ofairflow along the tube. This has been found to reduce the risk ofaccumulated secretions being loosened by airflow along the tube.

The length of the inner cannula 2 is chosen to be longer than the outertube 1 so that, when the patient end of the inner cannula is flush withthe patient end of the outer tube 1, a portion 22 at the machine end ofthe cannula projects from the machine end of the outer tube. Thisportion 22 is flexible relative to the outer tube and is typically about40-50 mm long. At its machine end, the cannula 2 has a coupling 23 bywhich the assembly is connected via tubing 30 to a ventilator 31.

The flexible nature of the portion 22 means that the tubing 30 can beled away from the tracheostomy in any direction. This avoids the needfor using a separated angled coupling or flexible interconnectionbetween the assembly and ventilation tubing 30. It also prevents unduestress being exerted on the tracheostomy.

The inner cannula 2 may have a stop (not shown) on its outer surface,which is located to be positioned at the flange 14 of the outer tube 1,when the patient end of the inner cannula is flush with the patient endof the outer tube. The stop may be arranged to seal with the flange, orin the machine end of the outer tube 1, to prevent passage of gasbetween the outside of the inner cannula and the inside of the outertube.

It is not essential for the outer surface of the cannula to be providedby a filament. Instead, as shown in FIG. 3, the outer surface could beprovided by a continuous layer 32 of a relatively low friction plasticsmaterial such as a polyolefin, for example, a low density polyethyleneor polypropylene. The outer layer 32 may be coextruded with the innerlayer 33 which may be of PVC. The tube of FIG. 3 will be more prone tokinking than that of FIG. 2 making it less suitable for providing aflexible coupling at the machine end of the outer tube.

It will be appreciated that the assembly could be an endotracheal tubeassembly instead of a tracheostomy tube assembly.

We claim:
 1. A tracheal tube assembly for use in ventilation of a patient, said assembly being sized for location in the trachea of a patient and comprising an outer tube and an inner cannula that is insertable within and removable from the outer tube, said inner cannula having an inner surface of a first material to which respiratory secretions will cling, and an outer surface of a second material that is different from said first material and provides said outer surface with a lower coefficient of friction than said inner surface to facilitate insertion of said inner cannula into, and removal of said inner cannula from, said outer tube.
 2. A tracheal tube assembly according to claim 1 wherein said outer surface is a continuous layer of said second material.
 3. A tracheal tube assembly according to claim 1, wherein said outer surface is provided by at least one filament extending around the outside of the cannula.
 4. A tracheal tube assembly according to claim 3, wherein said filament extends helically around the tube.
 5. A tracheal tube assembly according to claim 3 or 4, wherein said filament is of a metal.
 6. A tracheal tube assembly according to any one of claims 1 to 4, wherein said outer surface is provided by a low friction plastics material.
 7. A tracheal tube assembly according to any one of claims 1 to 4 wherein said inner surface is smooth.
 8. A tracheal tube assembly according to any one of claims 1 to 4 wherein said inner surface (20, 30) is of a flexible plastics material.
 9. A tracheal tube assembly according to claim 8, wherein said inner surface is PVC.
 10. A tracheal tube assembly according to any one of claims 1 to 4 wherein the inner cannula has a machine end that projects beyond a machine end of the outer tube and provides a flexible portion, the inner cannula having a coupling on its machine end. 